There has been a malicious worm created that can cause harm to those that use SSH to log into their phone. This is only for those that have OpenSSH installed and use something like Putty, Cyberduck or WinSCP on your computer and login to manage files through one of those programs. The default password is usually set in these programs and needs to be changed to secure your phone. See this thread for easy instructions to change the password:
http://forums.macrumors.com/showthread.php?t=825280
http://forums.macrumors.com/showthread.php?t=825280